libstdc++: Use __builtin_operator_new when available [PR94295]

Message ID YPcnbZWstQpfdTFW@redhat.com
State New
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  • libstdc++: Use __builtin_operator_new when available [PR94295]
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Commit Message

Lewis Hyatt via Gcc-patches July 20, 2021, 7:43 p.m.
Clang provides __builtin_operator_new and __builtin_operator_delete,
which have the same semantics as ::operator new and ::operator delete
except that the compiler is allowed to elide calls to them. This changes
std::allocator to use those built-in functions so that memory allocated
by std::allocator can be optimized away when using Clang. This avoids an
abstraction penalty for using std::allocator to allocate storage rather
than a new-expression.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>


libstdc++-v3/ChangeLog:

	PR libstdc++/94295
	* include/ext/new_allocator.h (_GLIBCXX_OPERATOR_NEW)
	(_GLIBCXX_OPERATOR_DELETE, _GLIBCXX_SIZED_DEALLOC): Define.
	(allocator::allocate, allocator::deallocate): Use new macros.

Tested powerpc64le-linux.

The macros are ugly, but using #ifdef is unavoidable here. I think
this is less ugly than the laternative ways to do this.

Any objections to pushing this, or any better ideas for doing this?
commit f8c86589f2eab42c0888390bea7bceb8dc31d92b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jul 19 16:43:11 2021

    libstdc++: Use __builtin_operator_new when available [PR94295]
    
    Clang provides __builtin_operator_new and __builtin_operator_delete,
    which have the same semantics as ::operator new and ::operator delete
    except that the compiler is allowed to elide calls to them. This changes
    std::allocator to use those built-in functions so that memory allocated
    by std::allocator can be optimized away when using Clang. This avoids an
    abstraction penalty for using std::allocator to allocate storage rather
    than a new-expression.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/94295
            * include/ext/new_allocator.h (_GLIBCXX_OPERATOR_NEW)
            (_GLIBCXX_OPERATOR_DELETE, _GLIBCXX_SIZED_DEALLOC): Define.
            (allocator::allocate, allocator::deallocate): Use new macros.

Comments

Lewis Hyatt via Gcc-patches July 22, 2021, 1:43 p.m. | #1
On 20/07/21 20:43 +0100, Jonathan Wakely wrote:
>Clang provides __builtin_operator_new and __builtin_operator_delete,

>which have the same semantics as ::operator new and ::operator delete

>except that the compiler is allowed to elide calls to them. This changes

>std::allocator to use those built-in functions so that memory allocated

>by std::allocator can be optimized away when using Clang. This avoids an

>abstraction penalty for using std::allocator to allocate storage rather

>than a new-expression.

>

>Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

>

>libstdc++-v3/ChangeLog:

>

>	PR libstdc++/94295

>	* include/ext/new_allocator.h (_GLIBCXX_OPERATOR_NEW)

>	(_GLIBCXX_OPERATOR_DELETE, _GLIBCXX_SIZED_DEALLOC): Define.

>	(allocator::allocate, allocator::deallocate): Use new macros.

>

>Tested powerpc64le-linux.

>

>The macros are ugly, but using #ifdef is unavoidable here. I think

>this is less ugly than the laternative ways to do this.

>

>Any objections to pushing this, or any better ideas for doing this?


Nobody said anything, so I've pushed it to trunk.


>commit f8c86589f2eab42c0888390bea7bceb8dc31d92b

>Author: Jonathan Wakely <jwakely@redhat.com>

>Date:   Mon Jul 19 16:43:11 2021

>

>    libstdc++: Use __builtin_operator_new when available [PR94295]

>

>    Clang provides __builtin_operator_new and __builtin_operator_delete,

>    which have the same semantics as ::operator new and ::operator delete

>    except that the compiler is allowed to elide calls to them. This changes

>    std::allocator to use those built-in functions so that memory allocated

>    by std::allocator can be optimized away when using Clang. This avoids an

>    abstraction penalty for using std::allocator to allocate storage rather

>    than a new-expression.

>

>    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

>

>    libstdc++-v3/ChangeLog:

>

>            PR libstdc++/94295

>            * include/ext/new_allocator.h (_GLIBCXX_OPERATOR_NEW)

>            (_GLIBCXX_OPERATOR_DELETE, _GLIBCXX_SIZED_DEALLOC): Define.

>            (allocator::allocate, allocator::deallocate): Use new macros.

>

>diff --git a/libstdc++-v3/include/ext/new_allocator.h b/libstdc++-v3/include/ext/new_allocator.h

>index 3fb893be152..7c48c820c62 100644

>--- a/libstdc++-v3/include/ext/new_allocator.h

>+++ b/libstdc++-v3/include/ext/new_allocator.h

>@@ -97,6 +97,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION

>       { return std::__addressof(__x); }

> #endif

>

>+#if __has_builtin(__builtin_operator_new) >= 201802L

>+# define _GLIBCXX_OPERATOR_NEW __builtin_operator_new

>+# define _GLIBCXX_OPERATOR_DELETE __builtin_operator_delete

>+#else

>+# define _GLIBCXX_OPERATOR_NEW ::operator new

>+# define _GLIBCXX_OPERATOR_DELETE ::operator delete

>+#endif

>+

>       // NB: __n is permitted to be 0.  The C++ standard says nothing

>       // about what the return value is when __n == 0.

>       _GLIBCXX_NODISCARD _Tp*

>@@ -121,34 +129,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION

> 	if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)

> 	  {

> 	    std::align_val_t __al = std::align_val_t(alignof(_Tp));

>-	    return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), __al));

>+	    return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp),

>+							   __al));

> 	  }

> #endif

>-	return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));

>+	return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp)));

>       }

>

>       // __p is not permitted to be a null pointer.

>       void

>-      deallocate(_Tp* __p, size_type __t __attribute__ ((__unused__)))

>+      deallocate(_Tp* __p, size_type __n __attribute__ ((__unused__)))

>       {

>+#if __cpp_sized_deallocation

>+# define _GLIBCXX_SIZED_DEALLOC(p, n) (p), (n) * sizeof(_Tp)

>+#else

>+# define _GLIBCXX_SIZED_DEALLOC(p, n) (p)

>+#endif

>+

> #if __cpp_aligned_new

> 	if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)

> 	  {

>-	    ::operator delete(__p,

>-# if __cpp_sized_deallocation

>-			      __t * sizeof(_Tp),

>-# endif

>-			      std::align_val_t(alignof(_Tp)));

>+	    _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n),

>+				     std::align_val_t(alignof(_Tp)));

> 	    return;

> 	  }

> #endif

>-	::operator delete(__p

>-#if __cpp_sized_deallocation

>-			  , __t * sizeof(_Tp)

>-#endif

>-			 );

>+	_GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n));

>       }

>

>+#undef _GLIBCXX_SIZED_DEALLOC

>+#undef _GLIBCXX_OPERATOR_DELETE

>+#undef _GLIBCXX_OPERATOR_NEW

>+

> #if __cplusplus <= 201703L

>       size_type

>       max_size() const _GLIBCXX_USE_NOEXCEPT

Patch

diff --git a/libstdc++-v3/include/ext/new_allocator.h b/libstdc++-v3/include/ext/new_allocator.h
index 3fb893be152..7c48c820c62 100644
--- a/libstdc++-v3/include/ext/new_allocator.h
+++ b/libstdc++-v3/include/ext/new_allocator.h
@@ -97,6 +97,14 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { return std::__addressof(__x); }
 #endif
 
+#if __has_builtin(__builtin_operator_new) >= 201802L
+# define _GLIBCXX_OPERATOR_NEW __builtin_operator_new
+# define _GLIBCXX_OPERATOR_DELETE __builtin_operator_delete
+#else
+# define _GLIBCXX_OPERATOR_NEW ::operator new
+# define _GLIBCXX_OPERATOR_DELETE ::operator delete
+#endif
+
       // NB: __n is permitted to be 0.  The C++ standard says nothing
       // about what the return value is when __n == 0.
       _GLIBCXX_NODISCARD _Tp*
@@ -121,34 +129,38 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
 	  {
 	    std::align_val_t __al = std::align_val_t(alignof(_Tp));
-	    return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), __al));
+	    return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp),
+							   __al));
 	  }
 #endif
-	return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));
+	return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp)));
       }
 
       // __p is not permitted to be a null pointer.
       void
-      deallocate(_Tp* __p, size_type __t __attribute__ ((__unused__)))
+      deallocate(_Tp* __p, size_type __n __attribute__ ((__unused__)))
       {
+#if __cpp_sized_deallocation
+# define _GLIBCXX_SIZED_DEALLOC(p, n) (p), (n) * sizeof(_Tp)
+#else
+# define _GLIBCXX_SIZED_DEALLOC(p, n) (p)
+#endif
+
 #if __cpp_aligned_new
 	if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
 	  {
-	    ::operator delete(__p,
-# if __cpp_sized_deallocation
-			      __t * sizeof(_Tp),
-# endif
-			      std::align_val_t(alignof(_Tp)));
+	    _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n),
+				     std::align_val_t(alignof(_Tp)));
 	    return;
 	  }
 #endif
-	::operator delete(__p
-#if __cpp_sized_deallocation
-			  , __t * sizeof(_Tp)
-#endif
-			 );
+	_GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n));
       }
 
+#undef _GLIBCXX_SIZED_DEALLOC
+#undef _GLIBCXX_OPERATOR_DELETE
+#undef _GLIBCXX_OPERATOR_NEW
+
 #if __cplusplus <= 201703L
       size_type
       max_size() const _GLIBCXX_USE_NOEXCEPT